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111 2003, Cisco Systems, Inc. All rights reserved.

Distance vector routing

RIP

IGRP


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Distance Vector Updates


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Problem: Routing Loops

Routing loops can occur when inconsistent routingtables are not updated due to slow convergence in achanging network.


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Problem: Counting to Infinity


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Solution: Defining a Maximum forInfinity


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Solution: Split Horizon


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Solution: Route Poisoning


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Solution: Triggered Updates


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Solution: Holddown Timers


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RIP Routing Process

Open standard version of RIP has evolved over the years from a Classful

Routing Protocol, RIP Version 1 (RIP v1), to a Classless Routing Protocol,

RIP Version 2 (RIP v2). RIP v2 enhancements include:

Ability to carry additional packet routing information.

Authentication mechanism to secure table updates.

Supports variable length subnet masking (VLSM).


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Configuring RIP

router rip

Network X.y.z.w

IP RIP triggered


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Configuring RIP (Contd)


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Using the ip classless Command

Destination network and Router A Fa0/1 and Fa0/2 are in the same IP major

network

A B


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RIP Configuration Issues

To avoid routing loops and counting to infinity, RIPuses the following:

Defining infinity (Route marked as unreachable)

Split horizon (Prevent reverse route)

Route poisoning & poison reverse

Triggered updates (Speed up Convergence)Hold-down timers


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The show ip protocols Command


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The show ip route Command


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Troubleshooting RIP Update Issues

debug ip rip

show ip protocols

show ip route rip

show ip interface

Show running-config

ping

traceroute


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Preventing Routing Updates throughan Interface


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RIP V2 Overview

All of the operational procedures, timers, and stability functions ofRIP v1 remain the same in RIP v2, with the exception of thebroadcast updates


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Basic RIP V2 Configuration

When RIP is first enabled on a Cisco router, the router listens for version1 and 2 updates but sends only version 1. To take advantage of version 2features, it is necessary to turn off version 1 support and enable version 2updates with the following command:


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Compatibility with RIP V1

RFC 1723 defines a compatibility switch with four settings,

which allows versions 1 and 2 to interoperate:

1. RIP v1, in which only RIP v1 messages are transmitted

2. RIP v1 Compatibility, which causes RIP v2 to broadcast its

messages instead of multicast them so that RIP v1 may

receive them

3. RIP v2, in which RIP v2 messages are multicast to

destination address 224.0.0.9

4. None, in which no updates are sent


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Compatibility with RIP V1(Contd)


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IGRP Features

By default, the IGRP routing protocol uses bandwidth and delay as metrics.

Additionally, IGRP can be configured to use a combination of variables to

determine a composite metric.


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IGRP Commands

Using router igrp and networkcommands to enable IGRP

Enabling IGRP on an IP-addressed

network

Monitoring IP packet flow using the showip protocol command

The show ip interfaces command

The show ip route command

The debug ip rip command


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IGRP Metrics

Bandwidth The lowest bandwidth valuein the path

Delay The cumulative interface delayalong the path

Reliability The reliability on the linktowards the destination as determined by

the exchange of keepalives Load The load on a link towards the

destination based on bits per second


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IGRP Stability Features

Holddowns, Split horizons, & Poison-reverseupdates


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Configuring IGRP


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Migrating RIP to IGRP

1. Verify existing routing protocol (RIP) onthe routers to be converted.

2. Configure IGRP on RouterA and RouterB

3. Entershow ip protocolson RouterAand RouterB

4. Entershow ip route on RouterA andRouterB


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Verifying IGRP Configuration

Some commands for checking IGRPconfiguration are as follows:

show interface interface

show running-config

show running-config interfaceinterface

show running-config | begin interface

interface

show running-config | begin igrp

show ip protocols


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Troubleshooting IGRP

The following commands are useful whentroubleshooting IGRP:

show ip protocols {summary}show ip route

debug ip igrp

debug ip igrp transactions

ping

traceroute

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